As for the conventional digital circuit design system, an LSI circuit design system and a printed circuit board (PCB) circuit design system have existed independently of each other, and an integrated EDA (electronic design automation) system from the LSI to the PCB has not existed.
In addition, in the process of the LSI design, no organic connection has been established between process design and logic design and no consistent integrated system has existed. Although information such as know-how's have been provided to take measures against EMI (electromagnetic interference), no consideration has been given to such an electromagnetic free design technique as to be able to be incorporated into the EDA design system.
Meanwhile, in relation to the printed circuit board circuit design system, a simplified design check tool such as an EMI rule checker has existed; however, no basic design rules have been established.
A conventional design technique in relation to a technique for suppressing digital equipment electromagnetic interference will next be described.
1. In designing a digital printed circuit board (PCB), a highly advanced EDA system is used mainly for the logic design. High-rate simulation in a design phase is targeted at logic and delay time.
2. In designing an LSI circuit, a lumped parameter system is responsible for design and analysis without any strict basis. In the lumped parameter system, a lumped parameter-system simulator represented by SPICE (simulation program with integrated circuit emphasis) performs analysis in relation to the electromagnetic interference.3. Conventionally, attention has been paid to signal wirings so as to tackle electromagnetic interference problems. This is because the signal wirings occupy the most parts of the printed circuit board (PCB) or a semiconductor LSI and high-frequency current exists on the signal wirings. To this end, an electromagnetic radiation simulator which simulates electromagnetic radiation from the PCB including the semiconductor LSI has been developed and put to practical use. However, the electromagnetic radiation simulator has a problem that the simulated electromagnetic radiation greatly differs from actually measured radiation, and the cause of the problem has not been cleared up. On the other hand, thanks to a recent study, it has been discovered for the first time that the major cause of the electromagnetic radiation from a digital equipment lies in a power supply circuit. For example, it has been discovered that it is possible to suppress electromagnetic radiation over the entire frequency band by 5 dB or more only by changing the power distribution of the PCB from conventional flat plate power distribution to wiring power distribution (see Japanese Patent Laid-Open Application Publication Nos. 9-139573 (to be referred to as “Document 1” hereinafter) and 11-40915 (to be referred to as “Document 2” hereinafter)). In addition, a chip capacitor conventionally used as a decoupling capacitor has its own resonance frequency in a low frequency band and has a problem of being incapable of following the speeding up. To solve this problem, a line component that decreases the impedance of a power supply line to a high frequency range has been invented (see Japanese Patent Laid-Open Application Publication No. 2001-119154 (to be referred to as “Document 3” hereinafter).